This invention relates to a switch device for self-extinguishing an electric arc struck across a pair of contact members by utilizing a gas expanded due to heat of the electric arc.
There have been recently developed simply, highly economical switch devices of the type including an amount of an arc extinguishing fluid such as gaseous sulfur hexafluoride (SF.sub.6) filling an arc extinguishing compartment space having a suitable volume and operative to put the arc extinguishing fluid under a high pressure through the utilization of the pressure increasing action resulting from thermal energy mainly provided by an electric arc itself and to extinguish the electric arc by delivering the fluid forming a high pressure source to an arc space in the process of decreasing the resulting arc current to a null magnitude.
However, it is well known that in arc self-extinguishing switch devices of conventional construction, the heat action of electric arcs for increasing the pressure becomes excessively large with an increase in arc current and the arc extinguishing fluid within the arc extinguishing compartment is put at elevated temperatures with the result that the arc extinguishing ability reduces with an increase in arc current. Also, such switch devices have been disadvantageous in that the rate of release of the high pressure source can not be readily controlled because the release of the high pressure source is accomplished by the movable contact member whose size is determined by a current normally flowing therethrough.
When arc self-extinguishing switch devices of the above type include a pressure increasing compartment having a volume and a pressure releasing opening formed to be fitted for the interruption of high short circuiting currents, the resulting pressure increasing action is small with relatively low currents such as currents somewhat higher than the load current because thermal energy of the electric arc struck upon the separation of contact members generally is low. In order to attain sufficiently the pressure increasing action at low currents, it is necessary to make the volume of the pressure increasing compartment small and the pressure releasing opening also small. However, if this is done, the pressure increasing compartment having a small volume suitable for interrupting low currents has been disadvantageous in that the temperatures within the pressure increasing and arc extinguishing compartments rises higher than is necessary. This has permitted the arc extinguishing fluid to be rather ionized thereby to promote the growth of the electric arc resulting in the arc extinguishing function being disabled.
Accordingly it is a general object of the present invention to eliminate the disadvantages of the prior art practice as above described.
It is an object of the present invention to provide a new and improved arc self-extinguishing switch device capable of controlling independently a current capacity and an interrupting performance.